Unless -enable-resilient-objc-class-stubs is passed in, these cases
are not supported, so now we diagnose them instead of asserting or
failing to link.
Note the behavior change here; classes with resilient ancestry were
previously isObjC(). However this is wrong since isObjC() means
"statically visible to Objective-C via the generated header".
After this patch, isObjC() only returns true for a class with resilient
ancestry if -enable-resilient-objc-class-stubs is passed in.
In-place initialization means the class has a symbol we can reference
from the category, so there's nothing to do on the IRGen side.
For JIT mode, we just need to realize the class metadata by calling an
accessor instead of directly referencing the symbol though.
If there was any requirements in the @objc protocol, the user got an error in
some form (a complaint about those requirements), but giving the direct error is
better, and handles @objc protocol with no requirements.
Also, fix a hole in that existing @objc method check: in `class Outer<T> { class
Inner {} }`, Inner should be considered generic, but the loop that was checking
for this didn't consider it.
Fixes https://bugs.swift.org/browse/SR-7370 and rdar://problem/39239512.
